The use of communication systems having mobile devices or mobile station systems which communicate with a hardwired network, such as a local area network (LAN) or a wide area network (WAN), has become widespread. For example, retail stores and warehouse use communication systems with mobile data terminals to track inventory and replenish stock. Manufacturing facilities employ these for tracking parts, completed products and defects. Such systems are also utilized for cellular telephone communications to allow users with wireless telephones to roam across large geographical regions while retaining telephonic access. Paging networks utilize cellular communications systems to enable a user carrying a pocket sized pager to be paged anywhere within a geographic region. A typical wireless communication system includes a number of fixed access points interconnected by a cable medium often referred to as a system backbone or distribution system. An access point is a device that typically forms a bridge between a wired network and one or more mobile station systems.
Recently a standard for wireless local area networks (WLANs) known as the IEEE 802.11 standard has been adopted. The IEEE 802.11 standard for WLANs is a standard for systems that operate in the 2,400–2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The IEEE 802.11 RF transmissions use multiple signaling schemes (modulations) at different data rates to deliver a single data packet between wireless systems. The latest IEEE 802.11 wireless LAN uses a band of frequencies near 2.4 Ghz for direct sequence spread spectrum transmissions. Another recently adopted short-range standard has evolved known as the Bluetooth standard. The Bluetooth standard is a low-cost short range wireless connection which uses much of the same range of frequencies for its frequency-hopping spread spectrum transmissions as the IEEE 802.11 standard. Consequently, there is expected to be considerable interference between the two systems.
Recently, a revised standard of the IEEE 802.11 has evolved referred to as the IEEE 802.1b standard. The IEEE 802.11b standard has a high rate DSSS Physical layer that uses a portion of radio frequency spectrum in the 2.4 GHz band. In the United States this spectrum has been allocated by the FCC to Industrial Scientific and Medical applications. The wireless medium is shared between the mobile stations in a manner defined by the IEEE 802.11b standard. Many devices other than IEEE 802.11b wireless LANs can operate in the 2.4 GHz ISM frequency band. Examples of such systems include microwave ovens, cordless telephones, Bluetooth personal area networks, short range consumer video transmitters, wireless LAN products designed for FHSS, or non 802.11 physical layer operation, wireless telemetry and control systems and malfunctioning or unauthorized 802.11 systems.
When such devices are introduced into a physical area served by an IEEE 802.11b 2.4 GHz DSSS wireless LAN, performance of the LAN will be degraded or totally disrupted. When such a disruption takes place it may be very difficult to locate the source of the interference, given the transient nature of the interference, and the physical area in which the source may be located. Digital communication over a wireless medium is intrinsically error prone so protocols such as 802.11 protocol include many built in mechanisms for working in the presence of interferes. These include automatic frame retransmission, automatic rate reduction, frame fragmentation schemes and physical layer spread spectrum modulation. Detecting interferers is conventionally performed by means of test equipment such as a spectrum analyzer which may be a portable handheld device with a directional antenna to aid in location of the interference.
The problem of detecting and removing wireless network interferers is analogous to that of network debug in the early days of shared wired Ethernet, where a faulty node could prevent operation of systems on the entire wired segment. Debugging such problems often required that a technician visit, and temporarily isolate, each node. This was a disruptive and time-consuming task. In a wireless environment, the difficulty of the debug task is greater, since the cause of the problem may not be located near any of the wireless nodes, and possibly not even within the premises of the networked equipment.